Film Developer Calculator (Dilution, Tank Volume, Temperature & Push/Pull Time)
Mix black-and-white film developer for your tank — concentrate and water for any dilution, the minimum concentrate per roll — and correct the development time from the 20 °C chart time for your actual temperature and for pushing or pulling, with the full process timeline.
How it works
concentrate = tank ÷ (parts + 1); water = tank − concentrate · time = chart time × 10^(−0.032 × (T − 20 °C)) × 1.4^(stops pushed) · minimum concentrate per roll: HC-110 6 mL, Rodinal 10 mL, DD-X 60 mL, XTOL/D-76 100 mL of stock
Development is chemistry with a clock: the same film and developer give a different negative if the bath is warmer, more dilute or left longer. Data sheets quote a time at 20 °C, and the standard correction is about 7% less time per degree warmer (the manufacturers' curves are close to a straight line on a log scale). Pushing — shooting the film at a higher speed — is made up in the developer with roughly 40% more time per stop. The other quiet failure is too little developer: highly diluted developers exhaust if the tank does not hold enough concentrate for the film area, so the minimum per roll matters as much as the ratio.
Worked example
HC-110 dilution B in a 300 mL single-reel tank: 9.4 mL of syrup + 291 mL water, comfortably above the 6 mL-per-roll minimum. A chart time of 6:30 at 20 °C becomes about 5:40 at 22 °C; the same film pushed one stop would need about 7:50 at 22 °C, and at 24 °C the box-speed time drops to 4:50 — close to the 5-minute floor where uneven development starts.
Frequently asked questions
How exact does the temperature need to be?
Within about half a degree for repeatable results — a one-degree error is a 7% time error, roughly a third of a grade of contrast. Use a glass or digital thermometer checked against another, and keep stop, fix and wash within a few degrees of the developer to avoid reticulation.
Can I re-use developer?
One-shot developers (Rodinal, HC-110 dilutions, DD-X diluted, XTOL 1+1) are discarded after each use. Stock D-76/XTOL/ID-11 can be re-used with a 10–15% time increase per roll up to the stated capacity, but consistency suffers; most home users dilute and discard.
Why did my highlights come out thin even though the time was right?
Usually developer exhaustion: a high dilution in a small tank with two rolls did not contain enough active concentrate. Check the minimum concentrate per roll (Rodinal 10 mL, HC-110 6 mL, XTOL 100 mL stock) and mix a larger volume or a stronger dilution.
Related calculators
Darkroom figures are starting points. Film, developer batch, agitation, water and thermometer accuracy all shift results — run a test roll or strip, keep notes, and adjust from your own results.